Instrument HB 24449-C for FIAT A 22 R Aviation Engine, Savoia Marchetti - SM 55, circa 1930

Instrument HB 24449-C for FIAT A 22 R aviation engine, made by FIAT spa in 1930, installed on the Savoia-Marchetti SM55, in use by the Italian Royal Air Force.

This tool was designed to check the alignment of the propeller shaft in relation to its pinion. In fact, following impacts suffered by the propeller, a careful examination of the engine frame and gearbox was essential. Once the check had been carried out, and no signs of damage had been detected, it was necessary to ascertain whether the alignment of the propeller shaft was within the established tolerance limits.

Displacements of the gearbox and the propeller shaft could occur due to the curvature of the propeller shaft, as well as the deformation of the bearing housings that supported the shaft itself, resulting in an altered alignment of the propeller shaft in relation to the its pinion. The HB 24449-C check tool was used to ascertain whether these movements had occurred or not, without having to dismantle the engine.

In fact, this instrument made it possible to check the parallelism between a flat surface fixed at a right angle to the propeller shaft, and the lower face of the reduction gear box, and precisely of the flange placed on the reduction gear cover, on which the gear box was applied. double referral.

This exact instrument was specifically made to conform to various types of engines, in this case, this model was made to be adapted exclusively to the FIAT A 22 R aviation engines which were also installed on the Savoia-Marchetti SM55 seaplanes, employed in the legendary Atlantic crossing of 1933.

To confirm the charm of this instrument there is a plate bearing the name of the equally legendary Royal Airport (Idroscalo) "A. Brunetta" of Orbetello, from which the Atlantic fliers, led by Italo Balbo, took off.

It is plausible to consider that this instrument was on board one of the aircraft used for that cruise, since during the ditching planned during the established route, such accidents could occur (forced landing) which would consequently have caused problems with the propeller shaft, therefore, if the check (carried out on site) had given a negative result, the plane could have resumed flight without problems.

Complete instrument and in excellent storage conditions with its original case.

This instrument is believed to be the only one known to exist today.